1. Field of the Invention
The present invention relates to the treatment of smoking tobacco. In one respect, the present invention relates to the removal of nitrates, by dissolution, from tobacco, particularly burley tobacco. In a further respect, the present invention relates to the manufacture of a tobacco mixture for use in a smoking article.
2. Description of the Prior Art
It is known in the art to remove soluble undesirable material from smoking tobacco by use of a solvent.
For example, U.S. Pat. No. 3,145,717 issued on Aug. 25, 1964, to Osborne, et al, deals with a method of making a web of tobacco material and includes a water extraction step to separate water soluble constituents. This is accomplished by placing the tobacco in a closed tank with one to three parts of water per part of tobacco at 190.degree. Fahrenheit for one to two hours. Afterward, the water soluble constituents are separated from the tobacco by draining, pressing or centrifuging. The extract is reapplied at a later step in the process after the extract has been acidified and neutralized with potassium carbonate.
U.S. Pat. No. 3,646,943 issued on Mar. 7, 1972, to Blewitt is directed to a method for making reconstituted tobacco wherein the tobacco stems are washed to remove tobacco solubles prior to refining. The stems are crushed and placed in a tank with water at a ratio of 10 parts of water of one part of flattened stems. This mixture is agitated and allowed to soak for at least a half hour. During this soaking period the stem material rises to the top and the tobacco liquor containing the tobacco solubles, such as nitrates, is drawn off from the bottom of the tank. As the tobacco liquor is removed, it is replaced with fresh water. The stem-water mixture is then refined.
U.S. Pat. No. 3,690,328 issued on Sept. 12, 1972, to Quarenghi is directed to wet processing tobacco stems wherein the stems are completely soaked for 30 to 60 minutes in water to dissolve soluble constituents. Subsequently, the stems are mechanically opened and allowed to drain to a moisture content of 80% and then dried.
U.S. Pat. No. 3,874,392 issued on Apr. 1, 1975, is directed to extracting nitrous oxides from tobacco by boiling the tobacco in water for 15 minutes. The tobacco is next pressed to remove excess moisture, spread out to separate the fibers, and dried by heated air.
Nitrate salts are more concentrated in burley tobacco than in other types of tobacco commonly used in cigarettes. It is sometimes desirable to remove the nitrate salts from the tobacco.
All of the above-discussed methods involve a substantial amount of soaking time and drying time. Therefore, they are not well suited to an efficient manufacturing process. In addition, extended soaking can adversely affect the tobacco by, for example, breaking it down to a pulpy mass. Furthermore, the drying steps require the expenditure of energy, increasing the costs of manufacture.